Process for the conversion of sulphite waste liquors into tanning extracts



rammed-Janis,192s. i 1,,59Z,,0Z" UNITED STATES, PATENT: OFFICE.

' 'WEBSTER E. BYRON BAKER, or YORK H van, PENNSYLVANIA. raoonss .ron rim coNvERsIo or SULPHIT-E WASTE Lmnon-s rN'ro TANNING nx'rnAoTs.

No Drawing. 'Application file'd February 25, 1922. Serial Nb. 539,284. 7

The present invention consists of a new principal object-of this step is the volitilizaprocess, for the utilization of waste liquors t'ion of some of the undesirable or injurious from the manufacture of sulphite wood gaseous impurities or components. which act pulp.- The process has for its purpose the at least in part as acids, and which, if not. 6 preparation of an improved extract v,suitremoved, would make a greater addition of 60 able for tanning leather from said. liquors. the reagents in the following :step necessary. I Sulphite' waste liquors, as they are com- A further object is the oxidation of some 'monly called. consist of a mixture of orvery complex organic compounds present. .ganic.'cornpoundsderived from the portions As-an inevitable consequence of the spray of the .wood which are rendered soluble action thereis some evaporation and conseduring the process of cooking the chips unquent cooling of the liquor. der pressure in the digester by the sulphite- .T he second step in the process consists in rocess, thereby converting'theminto pulp: the collection of these sprayedliquors, and to bensed'for making paper. The cooking subsequenttrea-tment at a temperature of ,15 liquor, or cooking acid as it is'called. consubstantially not less than 80 to 85 centitains at the start of the process calcium grade with the oxide or hydroxide of 'an bisulphite, with "an excess of sulphurous alkaline earth metal In a tank provided with ac1d,'1n solution in such a manner that an efficient agitator, until the loosely comthe total sulphurous .acid present isequal bined sulphurv dioxide contained in the I to about. five perf cent, while that oomliquoris changed to the sulphiteotthealkabined with the lime or calciumas monoline earth metal, and until the hydrogen lOIl g lphite i about one per cent, or expressed concentration of the liquor is substantially as bisulphite, about two per cent. The wood such as is designated by the symbol or expres contains principally cellulose, lignin, carbosion pI-lzt). The first half or two thirds (not 25 hydrates, and other organic matter in small more iof the required treatment may be done quantities, and small amounts of inorganic in some respects advantageously with the or mineral matter. During the cooking equivalent amount of a carbonate of an alkaprocess the lignin, carbohydrates v and" orline earth metal,if this is desirable or cheapg-anic matter are to 'a very-large extent dis-- er, but the rate of reaction is affected unsolved. while the, cellulose is left as pulp, favorably, carbonate of an alkaline earth these changes being eif'ected-bythe cooking metal being considered an equivalent and acid, and proper steaming. and gas relieving as such included in the claims. When using conditions. y i a the oxide, it is always slaked, forming a The liquors coming fromthe digester hydroxide solution or, suspension. The hyw-i-th the finished pulp when it is discharged drdl ideis also always turnished in dis-- 00 into the blow pit, containing newly formed solved or suspended form. compounds known as lignosulphonic acids, The selection of the alkaline earth metal i and the lime salts of these acids, together oxide, hydroxide, or carbonate is governed with carbohydrates, sugars and an excess of by cost to a large extent, but disregarding 40 free s-ulphur-ous acid. and some compounds this factor the chemical consideration entercontaining very loosely combined sulphurous ing into the proposition are the solubilities acid, are generally wasted. These liquors. of the various treating compounds, and the the solid content of which represents about solubilities of the-products resulting there- 50% ot the weightof the wood, "-form the from. In this process it is most favorable .45 principal starting material for the process chemically to use thecompounds of those alabout to be described. The total solids conkaline earth metals which have the most centr'ation of these liquors isusually from soluble hydroxides, and which r'orm the -five-to eight per cent. least soluble sulphitcs andsulphates. From "The first 'step in the new process consists these considerations it is apparent that in 50 in collecting these, liquors while-still nearly order of maximum to minimum desirability boiling hot, filtering out any and all fibers the alkaline earths should be arranged in the and solid materials in suspension, and following order,'viz, barium, strontium,,calpumping while still very hot, through a very jcium and magnesium. The comparatively 'fine spray nozzle or nozzles into air under low cost of lime, and the relative insolubility sufficient pressureto produce amist. The of its sulphate and sulphitemake it quite tain only minimum bowl tvpe. which discharges satisfactory for the manufacture of a suitable commercial product at the present time. In step two one object is to accomplish. principally three things, (1) the removal by conversion into insoluble form of some of the sulphur present, whether it be in the form of sulphates, sulphites, SUlPhUIOLS acid gas, or loosely combined and reversible sulphurous acid, (2) the change of the. reaction of the liquor from acidic to basic, (3) the conversion into insoluble form of any such compounds which would take place at much slower rate at lower temperatures. It may be noted that the reagent used should eon amounts of iron.

The third step in the process consists of filtering the insoluble matter produced in the second step from the resulting liquor. Complete separation is desirable. and the separated liquor should preferably be .crystal clear. For this reason it is advisable to subjectthe liquor to sedimentation in any of the known sedimentation or thickening apparatus, or simply in a tank. for a sufficient time to settle the major portion of the larger particles. The supernatant liquor is drawn oil and passed througha filter capable of holding the finest precipitates. While I do not limit this procedure to any particular form of filtration apparatus, itwill be found preferable in most cases to usea high speed centrifugal of the unperforated basket or the clear liquid the basket or bowl without passing it through the cake, which is precipitated in a compact mass on the side of the bowl or basket, while the filtrate flows ,over the top of the basket or bowl, or out of the bottom. In step three the purpose is minimizing decompositon of the liquor in its subsequent treatment, and minimizing corrosion and the deposition of scale and incrustation in'the apparatus Furthermore, the resulting prodnet is purer, than it would be if filtration were not resorted to, and a valuable byfrom - product consisting mostly of mono-s'ulphites No appreciable most advantageous 1s recovered.

The fourth step consists of the concentra of the resulting clear liquor to about 50% solids content, without decomposition. ecomposition is prevented by avoiding and minimizing the exposure of the liquid to high temperature, particularly as the concentration progresses. IVhile any type of apparatus, or method of obtainingthese conditions may be employed,it will be found and most-economical to do this in a multiple effect vacuum evapo-. rator, most desirable.

The evaporator may be constructed of cast iron, with narrow steel tubes.

increment in iron content will be experienced if the rapid film type'is used. In step four, the object is principally conversion into commercial form, so that the above.

and of these the rapid film type is' the above mentioned concentrated extract with sulphuric acid until the extract reacts just very faintly acid to the indicator Congo red. which is preferably applied in the form of Congo red test paper. The sulphuric acid used should be of such a strength as to possess a density between 32 and 35 degrees Baum, at 15 degrees centigrade, and neither the con centrated extract northe acid at the time of mixing should be at a temperature in excess of forty degrees centigrade nor should a temperature in excess of 40 C. be allowed to thereupon develop. The acid should be added very slowly, and the agitation of the mass of extract should be very eilicient.

Furthermore the entire treatment should be conducted in a vessel so arranged that iron will not come into contact with the mixture. A bronze or lead lined circular tank, equipped with bronze or lead covered agitator and heating coil will be very suitable. In this manner contamination of the extract with iron will be avoided. Furthermore. if the original extract prior to the addition of sulphuric acid, should contain suiiicient iron to act detrimentally in the tanning of leather, the iron may be removed by any of the'lrnown methods. In step five one object is to convert the organic salts into the corresponding organic acids, which are really the tanning agents, and the simultaneous conversion of at least part of the basic constituents into insoluble form for subsequent removal. I

The sixth step in the process consists of the filtration of the resulting extract. so as to completely remove all the solid matter in suspension. Precautions must also be taken to avoid contaminating the extract at this stage, in the same manner as stated This process may be carried out in various ways, by the application of several types of filtration apparatus, among which I may mention filter presses. pressure filters, gravity filters and vacuum filters of the usual types of construction, but it will be found most advantageous in a great number of cases to employ a centrifugal filter or clarifier, similar to such as is used in the clarification of varnish and heavy bodied oils.

The filtration is conducted shortly after the r object is. purification of the final product,

In step six one.

and the removal of some compounds rwhich would injure leatherand "also cau'se'the denot is improved, and the teriorationgot the" final extract. Furthermore, a by-product consisting principally 'otcalci im sulphate} isrecovered; 1

, 'As a modificationjot the above procedure the liquors, prior, .be subjected 'to partial fermentation into ethyl alcohol by any of the known processes. This utilizes the fermentable sugars, and reduces the percentage of inert organic substances dissolved in the I resulting .tanning-extract.

The above process is'an iinprovement inasmuch as the qualityof the resulting. prodcost of manufac- 1 ture is lowered. For exampleftheresulting product may be used alone in the tanning of leather, or'in combination with certain .other tanning agents. The leather produced has I more dcsirable and more permanent qualities and characteristics than leather made aqua-sane tanniiig eirtr from'hides treatedwith extracts made from sulphite waste liquors in the past! tracts were applicable only in thedrumming in process, 'and ser'ved'more strictly as fillers than as tanning agents. Further- Y more, theproce ssrepresents improvement in the reduction of the amount of treating reagent necessary, and in the fact that the filtration and type of evaporation reduces the in p yi g. h liquo .1

mist' -int b the air te -remove gaseous componentsa to oxidize-- I o. th er components,

treatl "g.-Z he. Sprayedfliquor with alkaline decompose "the present inco liquor,

' biriati'on withthe substances 'd-to incr-ease'the' eliminadiss'olved from woo tion otflsulphura's m.ono-su'lphite and filter- .ing -the""basic liquor to remove theinsoluble constituents, concentrating the filtered treating the concentrated liquor with l a modicum of sulphuric acid to convert the ,equivalent organic salts -into corresponding organic acids'wh'ch are the tanning agents earth metal constitand to convert alkaline uents equivalent thereto into insoluble form,

and filtering the concentrated liquor to remove the insoluble constitutents.

. 2.- The process of converting sulphite liquors-into tanning extracts which consists "agitating to .85 to the-second step, may

'30 to 35 degrees about Soto-35': degrees B'aum.

The process of Past exreversible sulphurous acid in'filte'ring and" spraying the liquor while .nearlyl boiling in the form of a mist into the air to remove gaseous compounds which act as acids and to oxidize other compounds, the sprayed liquor at substantially degrees Centigrade with alkaline earth metaloxide compound until loosely combined sulphur dioxide is changed to the sulphite otthe alkaline earth metal and until the hydrogen ion concentration of the liquor is pH:9, filtering'the basic liquor to remove the insolublecons'tituents and concentrating 1t,

treating the concentratedliquor at less than 40 centigrade with sulphuIfiQ. acid between 32 and 35 degrees Beanie referred to until it reactsfaintly acid, 'and filtering at centigrade the resulting liquor to remove the insoluble constituents and'leave the tanning agent in solution of converting uors into tanning extracts which consists in removing sulphur and gaseous components and oxidizing'organiccompounds and chang ing the reaction otthe liquor from acidic to basic by spraying" it in the form of a m st and by treating it with alkaline earth metal.

compounds, removing insolublematter from the liquor, treating the resultant liquor with sulphuric acid-insufficient for producing sub-' stantial mineral acidity and sufficient to cause Congored test paper to become faintly blue to convert organic salts into corres sponding acids which are the tanning agents and to simultaneously convert basic constituents into insoluble iorm, and removing the insoluble basic constituents. I

g 4. The process of converting sulphite liquors into tanning extracts which consists in removing sulphur and gaseous components and oxidizing organic componds and changbasic. by spraying it at substantially boiling temperature in the form ofa mist and by treating it at substantially 80 to degrees centigrade with alkaline earth metal compounds, treating the resultant liquor at less than 40 degrees centigrade .With sulphuric acid from 32 to 35 degrees Baum to convert organic salts into corresponding acids which are the tanning agents and to simultaneously, convert basic constituents which were combined with them'into insoluble form, and removing. the insoluble basic constituents by filtration at from 35 to L0 degrees centigrade until the discharging extract will have a density of about 30 to 33 degrees Baum.

5." The process of converting sulphite liq u'ors into tanning. extracts which consists in changing the reaction of the liquor from acidic to basic and removing sulphur and undesirable constitucnts by neutralizing it with alkaline earth metal compounds, treating the resultant liquor with a modicum of sulphuric 80 15 degrees Centigrade sulphite liq [ing'the reactionof the liquor from acidic to acid and limiting the mineralacidit of the stituents into insolube form, and filtering the liquor'to subtantially the degree in icatable concentrated liquor to remove the insoluble by the turning point of longo red test paper to convert organic salts into corresponding acids which are the tanning agents and to convert basic constituents into insoluble form, and removing insoluble basic constituents by filtration. 7 V

6. The process of converting sulphite liq uors into tanning extracts which consists in spraying the liquor in the form of a mist into the air to remove gaseeus components and to oxidize other components, subjecting the sprayed liquor to partial fermentation into ethyl alcohol, recovering the alcohol, treating the residual liquor with alkaline earth metal oxide compound sutficient to de compose the reversible sulphurcus acid present in combination with the substances dissolved from Wood to increase the elimination of sulphur as mono-sulphite and to convert sulphur into insoluble form, filtering the basic liquor to remove the insoluble constituents, concentrating the filtered liquor, treating the concentrated liquor with sulphuric acid to convert the organic salts into corresponding organic acids which are the tanning agents and to convert the basic conconstituents.

The process of converting sulphite liquors into tanning extracts which consists in spraying the liquor in the fornrof a mist into the air to remove gaseous components and 'to oxidize other components, treating the sprayed liquor with a portion of the required quantity of alkaline earth metal oxide compounds to facilitate fermentation and filtering it, subjecting the sprayed liquor to partial fermentation into ethyl alcohol, recovering the alcohol, treating the residual liquor with the remainder of the required alkaline earth metal oxide compounds to convert sulphur into insoluble form, filtering the basic liquor to remove the insoluble constituents, concentrating the filtered liquor, treating the concentrated liquor with sulphuric acid to convert the or anic salts into cor responding organic aci s which are the tanning agents and to convert the basic constituents into insoluble form, and filtering the concentrated liquor to remove the insoluble constituents.

WEBSTER E. BYRON BAKER. 

